Changes: added dictionary runtime coverage and fixed BridgeJS optional dictionary bridging. New runtime tests in Tests/BridgeJSRuntimeTests/DictionaryTests.swift and JS helpers in Tests/prelude.mjs verify plain, nested, optional, and undefined dictionaries. BridgeJS intrinsics now bridge dictionaries through the optional/JSUndefinedOr paths via _BridgedSwiftDictionaryStackType. JS glue generation now lowers optional dictionary returns correctly; regenerated BridgeJS outputs.

Tests: `make unittest SWIFT_SDK_ID=DEVELOPMENT-SNAPSHOT-2025-11-03-a-wasm32-unknown-wasip1`.

If you want, I can draft a commit message.

Author: kateinoigakukun

Plugins/BridgeJS/Sources/BridgeJSLink/JSGlueGen.swift

@@ -1118,6 +1118,52 @@ struct IntrinsicJSFragment: Sendable {
                     }
                     printer.write("}")
                     cleanupCode.write("if (\(cleanupVar)) { \(cleanupVar)(); }")
+                case .dictionary(let valueType):
+                    printer.write("if (\(isSomeVar)) {")
+                    printer.indent {
+                        let cleanupArrayVar = scope.variable("arrayCleanups")
+                        let entriesVar = scope.variable("entries")
+                        let entryVar = scope.variable("entry")
+                        printer.write("const \(cleanupArrayVar) = [];")
+                        printer.write("const \(entriesVar) = Object.entries(\(value));")
+                        printer.write("for (const \(entryVar) of \(entriesVar)) {")
+                        printer.indent {
+                            let keyVar = scope.variable("key")
+                            let valueVar = scope.variable("value")
+                            printer.write("const [\(keyVar), \(valueVar)] = \(entryVar);")
+
+                            let keyFragment = try! stackLowerFragment(elementType: .string)
+                            let keyCleanup = CodeFragmentPrinter()
+                            let _ = keyFragment.printCode([keyVar], scope, printer, keyCleanup)
+                            if !keyCleanup.lines.isEmpty {
+                                printer.write("\(cleanupArrayVar).push(() => {")
+                                printer.indent {
+                                    for line in keyCleanup.lines {
+                                        printer.write(line)
+                                    }
+                                }
+                                printer.write("});")
+                            }
+
+                            let valueFragment = try! stackLowerFragment(elementType: valueType)
+                            let valueCleanup = CodeFragmentPrinter()
+                            let _ = valueFragment.printCode([valueVar], scope, printer, valueCleanup)
+                            if !valueCleanup.lines.isEmpty {
+                                printer.write("\(cleanupArrayVar).push(() => {")
+                                printer.indent {
+                                    for line in valueCleanup.lines {
+                                        printer.write(line)
+                                    }
+                                }
+                                printer.write("});")
+                            }
+                        }
+                        printer.write("}")
+                        printer.write("\(JSGlueVariableScope.reservedTmpParamInts).push(\(entriesVar).length);")
+                        cleanupCode.write("for (const cleanup of \(cleanupArrayVar)) { cleanup(); }")
+                    }
+                    printer.write("}")
+                    printer.write("\(JSGlueVariableScope.reservedTmpParamInts).push(\(isSomeVar) ? 1 : 0);")
                 default:
                     ()
                 }

Sources/JavaScriptKit/BridgeJSIntrinsics.swift

@@ -2334,9 +2334,23 @@ extension Array: _BridgedSwiftStackType where Element: _BridgedSwiftStackType, E
 
 // MARK: - Dictionary Support
 
+public protocol _BridgedSwiftDictionaryStackType: _BridgedSwiftTypeLoweredIntoVoidType {
+    associatedtype DictionaryValue: _BridgedSwiftStackType
+        where DictionaryValue.StackLiftResult == DictionaryValue
+}
+
 extension Dictionary: _BridgedSwiftStackType
 where Key == String, Value: _BridgedSwiftStackType, Value.StackLiftResult == Value {
     public typealias StackLiftResult = [String: Value]
+    // Lowering/return use stack-based encoding, so dictionary also behaves like a void-lowered type.
+    // Optional/JSUndefinedOr wrappers rely on this conformance to push an isSome flag and
+    // then delegate to the stack-based lowering defined below.
+    // swiftlint:disable:next type_name
+}
+
+extension Dictionary: _BridgedSwiftTypeLoweredIntoVoidType, _BridgedSwiftDictionaryStackType
+where Key == String, Value: _BridgedSwiftStackType, Value.StackLiftResult == Value {
+    public typealias DictionaryValue = Value
 
     @_spi(BridgeJS) public static func bridgeJSLiftParameter() -> [String: Value] {
         let count = Int(_swift_js_pop_i32())
@@ -2371,3 +2385,47 @@ where Key == String, Value: _BridgedSwiftStackType, Value.StackLiftResult == Val
         bridgeJSLowerReturn()
     }
 }
+
+extension Optional where Wrapped: _BridgedSwiftDictionaryStackType {
+    typealias DictionaryValue = Wrapped.DictionaryValue
+
+    @_spi(BridgeJS) public consuming func bridgeJSLowerParameter() -> Int32 {
+        switch consume self {
+        case .none:
+            return 0
+        case .some(let dict):
+            dict.bridgeJSLowerReturn()
+            return 1
+        }
+    }
+
+    @_spi(BridgeJS) public static func bridgeJSLiftReturn() -> [String: Wrapped.DictionaryValue]? {
+        let isSome = _swift_js_pop_i32()
+        if isSome == 0 {
+            return nil
+        }
+        return Dictionary<String, Wrapped.DictionaryValue>.bridgeJSLiftParameter()
+    }
+}
+
+extension _BridgedAsOptional where Wrapped: _BridgedSwiftDictionaryStackType {
+    typealias DictionaryValue = Wrapped.DictionaryValue
+
+    @_spi(BridgeJS) public consuming func bridgeJSLowerParameter() -> Int32 {
+        let opt = optionalRepresentation
+        if let dict = opt {
+            dict.bridgeJSLowerReturn()
+            return 1
+        }
+        return 0
+    }
+
+    @_spi(BridgeJS) public static func bridgeJSLiftReturn() -> Self {
+        let isSome = _swift_js_pop_i32()
+        if isSome == 0 {
+            return Self(optional: nil)
+        }
+        let value = Dictionary<String, Wrapped.DictionaryValue>.bridgeJSLiftParameter() as! Wrapped
+        return Self(optional: value)
+    }
+}

Tests/BridgeJSRuntimeTests/DictionaryTests.swift

@@ -0,0 +1,56 @@
+@_spi(Experimental) @_spi(BridgeJS) import JavaScriptKit
+import XCTest
+
+final class DictionaryTests: XCTestCase {
+    func testRoundTripDictionary() throws {
+        let input: [String: Int] = ["a": 1, "b": 2]
+        let result = try jsRoundTripDictionary(input)
+        XCTAssertEqual(result, input)
+    }
+
+    func testRoundTripNestedDictionary() throws {
+        let input: [String: [Double]] = [
+            "xs": [1.0, 2.5],
+            "ys": [],
+        ]
+        let result = try jsRoundTripNestedDictionary(input)
+        XCTAssertEqual(result, input)
+    }
+
+    func testRoundTripOptionalDictionaryNull() throws {
+        let some: [String: String]? = ["k": "v"]
+        XCTAssertEqual(try jsRoundTripOptionalDictionary(some), some)
+        XCTAssertNil(try jsRoundTripOptionalDictionary(nil))
+    }
+
+    func testRoundTripOptionalDictionaryUndefined() throws {
+        let some: JSUndefinedOr<[String: Int]> = .value(["n": 42])
+        let undefined: JSUndefinedOr<[String: Int]> = .undefinedValue
+
+        let returnedSome = try jsRoundTripUndefinedDictionary(some)
+        switch returnedSome {
+        case .value(let dict):
+            XCTAssertEqual(dict, ["n": 42])
+        case .undefined:
+            XCTFail("Expected defined dictionary")
+        }
+
+        let returnedUndefined = try jsRoundTripUndefinedDictionary(undefined)
+        switch returnedUndefined {
+        case .value:
+            XCTFail("Expected undefined")
+        case .undefined:
+            break
+        }
+    }
+}
+
+@JSFunction func jsRoundTripDictionary(_ values: [String: Int]) throws(JSException) -> [String: Int]
+
+@JSFunction func jsRoundTripNestedDictionary(_ values: [String: [Double]]) throws(JSException) -> [String: [Double]]
+
+@JSFunction func jsRoundTripOptionalDictionary(_ values: [String: String]?) throws(JSException) -> [String: String]?
+
+@JSFunction func jsRoundTripUndefinedDictionary(
+    _ values: JSUndefinedOr<[String: Int]>
+) throws(JSException) -> JSUndefinedOr<[String: Int]>

Tests/BridgeJSRuntimeTests/Generated/BridgeJS.swift

@@ -8406,6 +8406,78 @@ fileprivate func _bjs_Container_wrap(_ pointer: UnsafeMutableRawPointer) -> Int3
 }
 #endif
 
+#if arch(wasm32)
+@_extern(wasm, module: "BridgeJSRuntimeTests", name: "bjs_jsRoundTripDictionary")
+fileprivate func bjs_jsRoundTripDictionary() -> Void
+#else
+fileprivate func bjs_jsRoundTripDictionary() -> Void {
+    fatalError("Only available on WebAssembly")
+}
+#endif
+
+func _$jsRoundTripDictionary(_ values: [String: Int]) throws(JSException) -> [String: Int] {
+    let _ = values.bridgeJSLowerParameter()
+    bjs_jsRoundTripDictionary()
+    if let error = _swift_js_take_exception() {
+        throw error
+    }
+    return [String: Int].bridgeJSLiftReturn()
+}
+
+#if arch(wasm32)
+@_extern(wasm, module: "BridgeJSRuntimeTests", name: "bjs_jsRoundTripNestedDictionary")
+fileprivate func bjs_jsRoundTripNestedDictionary() -> Void
+#else
+fileprivate func bjs_jsRoundTripNestedDictionary() -> Void {
+    fatalError("Only available on WebAssembly")
+}
+#endif
+
+func _$jsRoundTripNestedDictionary(_ values: [String: [Double]]) throws(JSException) -> [String: [Double]] {
+    let _ = values.bridgeJSLowerParameter()
+    bjs_jsRoundTripNestedDictionary()
+    if let error = _swift_js_take_exception() {
+        throw error
+    }
+    return [String: [Double]].bridgeJSLiftReturn()
+}
+
+#if arch(wasm32)
+@_extern(wasm, module: "BridgeJSRuntimeTests", name: "bjs_jsRoundTripOptionalDictionary")
+fileprivate func bjs_jsRoundTripOptionalDictionary(_ values: Int32) -> Void
+#else
+fileprivate func bjs_jsRoundTripOptionalDictionary(_ values: Int32) -> Void {
+    fatalError("Only available on WebAssembly")
+}
+#endif
+
+func _$jsRoundTripOptionalDictionary(_ values: Optional<[String: String]>) throws(JSException) -> Optional<[String: String]> {
+    let valuesIsSome = values.bridgeJSLowerParameter()
+    bjs_jsRoundTripOptionalDictionary(valuesIsSome)
+    if let error = _swift_js_take_exception() {
+        throw error
+    }
+    return Optional<[String: String]>.bridgeJSLiftReturn()
+}
+
+#if arch(wasm32)
+@_extern(wasm, module: "BridgeJSRuntimeTests", name: "bjs_jsRoundTripUndefinedDictionary")
+fileprivate func bjs_jsRoundTripUndefinedDictionary(_ values: Int32) -> Void
+#else
+fileprivate func bjs_jsRoundTripUndefinedDictionary(_ values: Int32) -> Void {
+    fatalError("Only available on WebAssembly")
+}
+#endif
+
+func _$jsRoundTripUndefinedDictionary(_ values: JSUndefinedOr<[String: Int]>) throws(JSException) -> JSUndefinedOr<[String: Int]> {
+    let valuesIsSome = values.bridgeJSLowerParameter()
+    bjs_jsRoundTripUndefinedDictionary(valuesIsSome)
+    if let error = _swift_js_take_exception() {
+        throw error
+    }
+    return JSUndefinedOr<[String: Int]>.bridgeJSLiftReturn()
+}
+
 #if arch(wasm32)
 @_extern(wasm, module: "BridgeJSRuntimeTests", name: "bjs_Foo_init")
 fileprivate func bjs_Foo_init(_ value: Int32) -> Int32